1. Field of the Invention
This invention relates to improvements in a cylinder lock, and more particularly a cylinder lock associated with a key therefor, arranged to effectively prevent an illegal unlocking of the cylinder lock.
2. Description of the Prior Art
Hitherto a variety of cylinder locks are proposed and put into practical use. The cylinder locks include a so-called axially operated type lock which is generally arranged as follows: A lock cylinder is rotatably disposed inside a casing to form an annular key insertion hole therebetween. When a key having a cylindrical tip end section is inserted into the key insertion hole, tumbler-pins in the cylinder lock are slid axially thereby making the lock cylinder rotatable. Such a cylinder lock is advantageous as it can be set to many key chords. Additionally, in this cylinder lock, the key in its unlocked position can be extracted from the lock cylinder, thereby preventing leaving the cylinder lock unlocked. Accordingly, such cylinder locks have been extensively used for automatic vending machines, lockers, or the likes.
The internal structure of a typical one of the cylinder locks will be briefly explained with reference to FIG. 6. The cylinder lock includes a generally cylindrical casing 1' which is formed with a bore defined by its inner peripheral surface 2'. The casing 1' is provided at its left end with a generally cylindrical front wall 3' which radially inwardly projects over the inner peripheral surface 2' to form an annular step wall surface 4' perpendicular to the axis of the cylinder lock. The step wall surface 4' is located between the inner peripheral surface of the front wall 3' and the inner peripheral surface 2'. A cylindrical sleeve 5' is disposed at the right half section of the bore of the casing 1'. A hole 6' is formed throughout the casing 1' and the sleeve 5' and opened at the outer peripheral surface of the casing 1'. A fixing pin 7' is fitted in the hole 6', thereby fixing the sleeve 5' to the casing 1'. The left end face of the sleeve 5' forms an annular wall surface 8' perpendicular to the inner peripheral surface 2' of the casing 1'.
A plurality of under-pin holes 9' are formed at the annular wall surface 8' and extend axially to a closed bottom. An under-pin 11' is disposed in each under-pin hole 9'. Accordingly, each under-pin 11' is biased in a direction to project leftward over the annular wall surface 8' under the bias of a spring 10'.
A lock cylinder 12' is rotatably disposed in the bore of the casing 1' and formed at its tip end with a key guide section 12a'. An annular key insertion hole 13' is formed between the key guide section 12a' and the front wall 3' of the cylinder 1'. The lock cylinder 12' is formed at its central portion with a flange section 12b', which is in slidable contact with the annular wall surface 8'. The lock cylinder 12' has a shaft section 12c' which extends rightward from the flange section 12b' and is located inside the sleeve 5'. The shaft section 12c' projects rightward over the right end wall of the casing 1' to form an end portion. The end portion of the shaft section 12c' is formed at its outer peripheral surface with an external thread. The external thread is engaged with an internal thread of a nut 17'. A cam 14' is fixedly mounted the end portion of the shaft section 12c' of the key cylinder 12' and located between the casing 1' and the nut 17'.
The flange section 12b' of the lock cylinder 12' is formed with a plurality of tumbler-pin holes 15' which are locatable to agree respectively to the under-pin holes 9'. A plurality of tumbler-pins 16' are inserted and disposed respectively in the tumbler-pin holes 15'.
Under a locked condition of the cylinder lock, the tip end section of each under-pin 11' is inserted in or engaged with the tumbler-pin holes 15'. Therefore, the lock cylinder 12' cannot be rotated. When a key (not shown) is inserted into the key insertion hole 13', the contacting surface of each tumbler-pin 16' and the corresponding under-pin 11' is brought into agreement with a shear line or the annular wall surface 8', and the lock cylinder becomes rotatable. Then, a rotation of the key toward a unlocked position makes the cylinder lock unlocked.
However, drawbacks have been encountered in the above-discussed cylinder locks. That is, the tumbler-pins 16' can be seen through the key insertion hole 13' from the outside. Assuming that a complicated structure picking tool having a plurality of pushing rods is inserted into the key insertion hole 13', and then, the pushing rods push the respective tumbler-pins 16' upon being adjusted in their projection amount, an illegal unlock of the cylinder lock occurs. This type of lock renders difficult complete prevention in the case of theft.